Energy storage system utilizing compressed gas

ABSTRACT

An energy storage and recovery system employs air compressed utilizing power from an operating wind turbine. This compressed air is stored within one or more chambers of a structure supporting the wind turbine above the ground. By functioning as both a physical support and as a vessel for storing compressed air, the relative contribution of the support structure to the overall cost of the energy storage and recovery system may be reduced, thereby improving economic realization for the combined turbine/support apparatus. In certain embodiments, expansion forces of the compressed air stored within the chamber, may be relied upon to augment the physical stability of a support structure, further reducing material costs of the support structure.

BACKGROUND

Air compressed to 300 bar has energy density comparable to that oflead-acid batteries and other energy storage technologies. One source ofcompressed air is wind.

It is known that the efficiency of power generation from wind, improveswith increased height of elevation of the fan blades of the wind turbinefrom the ground. Such elevation, however, requires provision of a large,fixed structure of sufficient mechanical strength to safely support therelatively heavy structure of the turbine, including the blades, under avariety of wind conditions.

The expense of constructing and maintaining such a support structure isan inherent expense of the system, detracting from the overallprofitability of the wind generation device. Accordingly, there is aneed in the art for novel structures and methods for supporting a windturbine.

SUMMARY

An energy storage and recovery system employs air compressed utilizingpower from an operating wind turbine. This compressed air is storedwithin one or more chambers of a structure supporting the wind turbineabove the ground. By functioning as both a physical support and as avessel for storing compressed air, the relative contribution of thesupport structure to the overall cost of the energy storage and recoverysystem may be reduced, thereby improving economic realization for thecombined turbine/support apparatus. In certain embodiments, expansionforces of the compressed air stored within the chamber may be reliedupon to augment the physical stability of a support structure, furtherreducing material costs of the support structure.

An embodiment of a method in accordance with the present inventioncomprises storing compressed gas generated from power of an operatingwind turbine, within a chamber defined by walls of a structuresupporting the wind turbine.

An embodiment of an apparatus in accordance with the present inventioncomprises a support structure configured to elevate a wind turbine abovethe ground, the support structure comprising walls defining a chamberconfigured to be in fluid communication with a gas compressor operatedby the wind turbine, the chamber also configured to store gas compressedby the compressor.

An embodiment of an apparatus in accordance with the present inventioncomprises an energy storage system comprising a wind turbine, a gascompressor configured to be operated by the wind turbine, and a supportstructure configured to elevate the wind turbine above the ground, thesupport structure comprising walls defining a chamber in fluidcommunication with the gas compressor, the chamber configured to storegas compressed by the gas compressor. A generator is configured togenerate electrical power from expansion of compressed gas flowed fromthe chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified schematic representation of an embodiment of asystem in accordance with the present invention.

FIG. 1A shows a simplified top view of one embodiment of a planetarygear system which could be used in embodiments of the present invention.FIG. 1AA shows a simplified cross-sectional view of the planetary gearsystem of FIG. 1A taken along line 1A-1A′.

FIG. 2 is a simplified schematic representation of an alternativeembodiment of a system in accordance with the present invention.

FIG. 3 is a simplified schematic representation of an alternativeembodiment of a system in accordance with the present invention.

FIG. 3A is a simplified schematic representation of an alternativeembodiment of a system in accordance with the present invention.

FIG. 4 is a simplified schematic representation of an alternativeembodiment of a system in accordance with the present invention.

FIG. 5 is a simplified schematic representation of an alternativeembodiment of a system in accordance with the present invention.

While certain drawings and systems depicted herein may be configuredusing standard symbols, the drawings have been prepared in a moregeneral manner to reflect the variety implementations that may berealized from different embodiments.

DETAILED DESCRIPTION

As previously described, a wind turbine operates to capture wind energymore effectively the higher it is elevated above the ground. Inparticular, wind speed is roughly proportional to the seventh root ofthe height. Power is proportional to the cube of the wind speed, andalso proportional to the area of the wind turbine. A greater height, H,could theoretically allow a larger diameter turbine, giving areaproportional to H² and power proportional to H^(x), with x perhaps asgreat as 2 3/7. The support structure is thus a necessary element of thesystem. According to embodiments of the present invention, this supportstructure can perform the further duty of housing one or more chambersor vessels configured to receive and store compressed air generated fromoutput of the wind turbine.

Such a support structure for a wind turbine is initially well suited forthis task, as it is typically formed from an exterior shell thatencloses an interior space. This structure provides the desiredmechanical support for the wind turbine at the top, while not consumingthe large amount of material and avoiding the heavy weight that wouldotherwise be associated with an entirely solid supporting structure.

FIG. 1 shows a simplified schematic view of an embodiment of a system inaccordance with the present invention. Specifically, system 100comprises a nacelle 101 that is positioned on top of support tower 106.Nacelle 101 includes a wind turbine 102 having rotatable blades 104.

Nacelle 101 may be in rotatable communication (indicated by arrow 120)with support tower 106 through joint 111, thereby allowing the blades ofthe wind turbine to be oriented to face the direction of the prevailingwind. An example of a wind turbine suitable for use in accordance withembodiment of the present invention is the model 1.5 sle turbineavailable from the General Electric Company of Fairfield, Conn.

Upon exposure to wind 108, the blades 104 of the turbine 102 turn,thereby converting the power of the wind into energy that is output onlinkage 105. Linkage 105 may be mechanical, hydraulic, or pneumatic innature.

Linkage 105 is in turn in physical communication with a motor/generator114 through gear system 112 and linkage 103. Gear system 112 is also inphysical communication with compressor/expander element 116 throughlinkage 107. Linkages 103 and 107 may be mechanical, hydraulic, orpneumatic in nature.

The gear system may be configured to permit movement of all linkages atthe same time, in a subtractive or additive manner. The gear system mayalso be configured to accommodate movement of fewer than all of thelinkages. In certain embodiments, a planetary gear system may bewell-suited to perform these tasks.

Compressed gas storage chamber 118 is defined within the walls 118 a ofthe support tower. Compressor/expander 116 is in fluid communicationwith storage chamber 118 through conduit 109.

Several modes of operation of system 100 are now described. In one modeof operation, the wind is blowing, and demand for power on the grid ishigh. Under these conditions, substantially all of the energy outputfrom rotation of the blades of the turbine, is communicated throughlinkages 105 and 103 and gear system 112 to motor/generator 114 that isacting as a generator. Electrical power generated by motor/generator 114is in turn communicated through conduit 113 to be output onto the gridfor consumption. The compressor/expander 116 is not operated in thismode.

In another mode of operation, the wind is blowing but demand for poweris not as high. Under these conditions, a portion of the energy outputfrom rotation of the blades of the turbine is converted into electricalpower through elements 105, 112, 103, and 114 as described above.

Moreover, some portion of the energy output from the operating turbineis also communicated through linkages 105 and 107 and gear system 112 tooperate compressor/expander 116 that is functioning as a compressor.Compressor/expander 116 functions to intake air, compress that air, andthen flow the compressed air into the storage chamber 118 located in thesupport tower. As described below, energy that is stored in the form ofthis compressed air can later be recovered to produce useful work.

Specifically, in another mode of operation of system 100, thecompressor/expander 116 is configured to operate as an expander. In thismode, compressed air from the storage chamber is flowed through conduit109 into the expander 116, where it is allowed to expand. Expansion ofthe air drives a moveable element that is in physical communication withlinkage 107. One example of such a moveable element is a piston that ispositioned within a cylinder of the compressor/expander 116.

The energy of actuated linkage 107 is in turn communicated through gearsystem 112 and linkage 103 to motor/generator 114 that is acting as agenerator. Electrical power generated by motor/generator as a result ofactuation of linkage 103, may in turn be output to the power gridthrough conduit 113.

In the mode of operation just described, the wind may or may not beblowing. If the wind is blowing, the energy output by thecompressor/expander 116 may be combined in the gear system with theenergy output by the turbine 112. The combined energy from these sources(wind, compressed air) may then be communicated by gear system 112through linkage 103 to motor/generator 114.

In still another mode of operation, the wind may not be blowing andpower demand is low. Under these conditions, the compressor/expander 116may operate as a compressor. The motor/generator 114 operates as amotor, drawing power off of the grid to actuate the compressor/expander116 (functioning as a compressor) through linkages 103 and 107 and gearsystem 112. This mode of operation allows excess power from the grid tobe consumed to replenish the compressed air stored in the chamber 118for consumption at a later time.

Embodiments of systems which provide for the efficient storage andrecovery of energy as compressed gas, are described in the U.S.Provisional Patent Application No. 61/221,487 filed Jun. 29, 2009, andin the U.S. nonprovisional patent application Ser. No. 12/695,922 filedJan. 28, 2010, both of which are incorporated by reference in theirentireties herein for all purposes. However, embodiments of the presentinvention are not limited to use with these or any other particulardesigns of compressed air storage and recovery systems. Alsoincorporated by reference in its entirety herein for all purposes, isthe provisional patent application No. 61/294,396, filed Jan. 12, 2010.

As previously mentioned, certain embodiments of the present inventionmay favorably employ a planetary gear system to allow the transfer ofmechanical energy between different elements of the system. Inparticular, such a planetary gear system may offer the flexibility toaccommodate different relative motions between the linkages in thevarious modes of operation described above.

FIG. 1A shows a simplified top view of one embodiment of a planetarygear system which could be used in embodiments of the present invention.FIG. 1AA shows a simplified cross-sectional view of the planetary gearsystem of FIG. 1A taken along line 1A-1A′.

Specifically, planetary gear system 150 comprises a ring gear 152 havinga first set of teeth 154 on an outer periphery, and having a second setof teeth 156 on an inner portion. Ring gear 152 is engaged with, andmoveable in either direction relative to, three other gear assemblies.

In particular, first gear assembly 140 comprises side gear 142 that ispositioned outside of ring gear 152, and is fixed to rotatable shaft 141which serves as a first linkage to the planetary gear system. The teethof side gear 142 are in mechanical communication with the teeth 154located on the outer periphery of the ring gear. Rotation of shaft 141in either direction will translate into a corresponding movement of ringgear 152.

A second gear assembly 158 comprises a central (sun) gear 160 that ispositioned inside of ring gear 152. Central gear 160 is fixed torotatable shaft 162 which serves as a second linkage to the planetarygear system.

Third gear assembly 165 allows central gear 160 to be in mechanicalcommunication with the second set of teeth 156 of ring gear 152. Inparticular, third gear assembly 165 comprises a plurality of (planet)gears 164 that are in free rotational communication through respectivepins 167 with a (planet carrier) plate 166. Plate 166 is fixed to athird shaft 168 serving as a third linkage to the planetary gear system.

The planetary gear system 150 of FIGS. 1A-1AA provides mechanicalcommunication with three rotatable linkages 141, 162, and 168. Each ofthese linkages may be in physical communication with the various otherelements of the system, for example the wind turbine, a generator, amotor, a motor/generator, a compressor, an expander, or acompressor/expander.

The planetary gear system 150 permits movement of all of the linkages atthe same time, in a subtractive or additive manner. For example wherethe wind is blowing, energy from the turbine linkage may be distributedto drive both the linkage to a generator and the linkage to acompressor. In another example, where the wind is blowing and demand forenergy is high, the planetary gear system permits output of the turbinelinkage to be combined with output of an expander linkage, to drive thelinkage to the generator.

Moreover, the planetary gear system is also configured to accommodatemovement of fewer than all of the linkages. For example, rotation ofshaft 141 may result in the rotation of shaft 162 or vice-versa, whereshaft 168 is prevented from rotating. Similarly, rotation of shaft 141may result in the rotation of only shaft 168 and vice-versa, or rotationof shaft 162 may result in the rotation of only shaft 168 andvice-versa. This configuration allows for mechanical energy to beselectively communicated between only two elements of the system, forexample where the wind turbine is stationary and it is desired tooperate a compressor based upon output of a motor.

Returning to FIG. 1, certain embodiments of compressed gas storage andrecovery systems according to the present invention may offer a numberof potentially desirable characteristics. First, the system leveragesequipment that may be present in an existing wind turbine system. Thatis, the compressed air energy storage and recovery system may utilizethe same electrical generator that is used to output power from the windturbine onto the grid. Such use of the generator to generate electricalpower both from the wind and from the stored compressed air, reduces thecost of the overall system.

Another potential benefit associated with the embodiment of FIG. 1 isimproved efficiency of power generation. Specifically, the mechanicalenergy output by the rotating wind turbine blades, is able to becommunicated in mechanical form to the compressor without the need forconversion into another form (such as electrical energy). By utilizingthe output of the power source (the wind turbine) in its nativemechanical form, the efficiency of transfer of that power intocompressed air may be enhanced.

Still another potential benefit associated with the embodiment of FIG. 1is a reduced number of components. In particular, two of the elements ofthe system perform dual functions. Specifically, the motor/generator canoperate as a motor and as a generator, and the compressor/expander canoperate as a compressor or an expander. This eliminates the need forseparate, dedicated elements for performing each of these functions.

Still another potential benefit of the embodiment of FIG. 1 is relativesimplicity of the linkages connecting various elements with movingparts. Specifically, in the embodiment of FIG. 1, the turbine, the gearsystem, the motor/generator, and the compressor/expander are all locatedin the nacelle. Such a configuration offers the benefit of compatibilitywith a rotational connection between a nacelle and the underlyingsupport structure. In particular, none of the linkages between theelements needs to traverse the rotating joint, and thus the linkages donot need to accommodate relative motion between the nacelle and supportstructure. Such a configuration allows the design and operation of thoselinkages to be substantially simplified.

According to alternative embodiments, however, one or more of the gearsystem, the compressor/expander, and the motor/generator may bepositioned outside of the nacelle. FIG. 2 shows a simplified view ofsuch an alternative embodiment of a system 200 in accordance with thepresent invention.

In this embodiment, while the turbine 202 is positioned in the nacelle201, the gear system 212, compressor/expander 216, and motor generator214 are located at the base of the tower 206. This placement is madepossible by the use of an elongated linkage 205 running between turbine202 and gear system 212. Elongated linkage 205 may be mechanical,hydraulic, or pneumatic in nature.

The design of the embodiment of FIG. 2 may offer some additionalcomplexity, in that the linkage 205 traverses rotating joint 211 andaccordingly must be able to accommodate relative motion of the turbine202 relative to the gear system 212. Some of this complexity may bereduced by considering that linkage 205 is limited to communicatingenergy in only one direction (from the turbine to the gear system).

Moreover, the cost of complexity associated with having linkage 205traverse rotating joint 211, may be offset by the ease of access to themotor/generator, compressor/expander, and gear system. Specifically,these elements include a large number of moving parts and are subject towear. Positioning these elements at the base of the tower (rather thanat the top) facilitates access for purposes of inspection andmaintenance, thereby reducing cost.

Still other embodiments are possible. For example, while FIG. 2 showsthe gear system, motor/generator, and compressor/expander elements asbeing housed within the support structure, this is not required. Inother embodiments, one or more of these elements could be locatedoutside of the support structure, and still communicate with the windturbine through a linkage extending from the support tower. In suchembodiments, conduits for compressed air and for electricity, andmechanical, hydraulic, or pneumatic linkages could provide for thenecessary communication between system elements.

Embodiments of the present invention are not limited to the particularelements described above. For example, while FIGS. 1 and 2 showcompressed gas storage system comprising compressor/expander elementsand motor/generator elements having combined functionality, this is notrequired by the present invention.

FIG. 3 shows an alternative embodiment a system 300 according to thepresent invention, utilizing separate, dedicated compressor 350,dedicated expander 316, dedicated motor 354, and dedicated generator 314elements. Such an embodiment may be useful to adapt an existing windturbine to accommodate a compressed gas storage system.

Specifically, pre-existing packages for wind turbines may feature thededicated generator element 314 in communication with the turbine 302through gear system 312 and linkages 303 and 305. Generator 314,however, is not designed to also exhibit functionality as a motor.

To such an existing configuration, a dedicated expander 316, a dedicatedcompressor 350, a dedicated motor 354, linkages 307 and 373, and conduit370 may be added to incorporate a compressed gas storage system. In oneembodiment, a dedicated expander 316 may be positioned in the nacelle301 in communication with the gear system 312 through linkage 307.Dedicated expander 316 is in fluid communication with a top portion ofthe compressed gas storage chamber 318 defined within the walls 306 a ofsupport tower 306 through conduit 309.

Dedicated compressor 350 and a dedicated motor 354 are readily included,for example at or near the base of the support tower, therebyfacilitating access to these elements. Dedicated compressor 350 is influid communication with storage chamber 318 through conduit 370, and inphysical communication with dedicated motor 354 through linkage 372.Dedicated motor 354 is in turn in electronic communication with thegenerator and/or grid to receive power to operate the compressor toreplenish the supply of compressed gas stored in the chamber 318.

As shown in FIG. 3, this embodiment may further include an optionalelongated mechanical, hydraulic, or pneumatic linkage 374 extendingbetween the gear system 312 in the nacelle 301, and the dedicatedcompressor 350 located outside of the nacelle 301. Such a linkage wouldallow the dedicated compressor to be directly operated by the output ofthe turbine, avoiding losses associated with converting mechanical intoelectrical form by the dedicated generator, and re-converting theelectrical power back into mechanical form by the dedicated motor inorder to operate the compressor.

FIG. 3A shows a simplified view of yet another embodiment of a system inaccordance with the present invention. In the embodiment of the system380 of FIG. 3A, only the turbine 382, linkage 383, and dedicatedcompressor 386 elements are located in the nacelle 381 that ispositioned atop support tower 396. Dedicated compressor 386 is incommunication with the turbine through linkage 383 (which may bemechanical, hydraulic, or pneumatic), which serves to drive compressionof air by the dedicated compressor. Compressed air output by thededicated compressor is flowed through conduit 389 across joint 391 intochamber 398 present in the support tower 396.

The remaining elements are positioned outside of the nacelle, either inthe support tower, or alternatively outside of the support tower. Forexample, a dedicated expander or expander/compressor 388 is incommunication with the chamber 398 defined within walls 396 a, toreceive compressed air through conduit 393. Element 388 is configured toallow expansion of the compressed air, and to communicate energyrecovered from this expansion through linkage 392 to generator orgenerator/motor 384. Element 384 in turn operates to generateelectricity that is fed onto the grid.

The embodiment of FIG. 3A can also function to store energy off of thegrid. Where element 384 is a generator/motor and element 388 is anexpander/compressor, element 384 may operate as a motor to drive element388 operating as a compressor, such that air is compressed and flowedinto chamber 398 for storage and later recovery.

The embodiment of FIG. 3A offers a potential advantage in that power istransported from the top to the bottom of the tower utilizing thechamber, without requiring a separate elongated linkage or conduit.Another possible advantage of the embodiment of FIG. 3A is a reductionin the weight at the top of the tower. While this embodiment may incurlosses where the mechanical power output of the turbine is convertedfirst into compressed air and then back into mechanical power fordriving the generator, such losses may be offset by a reduction inweight at the top of the tower, allowing the tower to be higher and toaccess more wind power.

The present invention is not limited to a support structure having anyparticular shape. In the particular embodiments shown in FIGS. 1 and 2,the support structure exhibits a cross-sectional shape that varies alongits length. For example, the support structure 106 is wide at its base,and then tapers to a point at which it meets the wind turbine. Byallocating material to where it will best serve the supporting function,such a design minimizes materials and reduces cost.

However, the present invention also encompasses supporting structureshaving other shapes. For example, FIG. 4 shows a support structure 400comprising a hollow tube having a circular or elliptical cross sectionthat is substantially uniform. The walls 400 a of this hollow tube 400in turn define a chamber 402 for storing compressed gas. While possiblyutilizing more mass, such a tube is a simpler structure that is employedfor a various applications in many other industries. Accordingly, such atube is likely available at a relatively low price that may offset anygreater material cost.

Still further alternative embodiments are possible. For example, incertain embodiments a support structure may be designed to takeadvantage of the forces exerted by the compressed air stored therein, inorder to impart additional stability to the support structure.

Thus, FIG. 5 shows an embodiment wherein the support structure 500comprises a portion 506 a having thinner walls 506 b exhibiting lessinherent strength than those of the prior embodiments. This reducedstrength may be attributable to one or more factors, including but notlimited to, use of a different design or shape for the support, use of areduced amount of material in the support, or use of a differentmaterial in the support.

According to embodiments of the present invention, however, anyreduction in the inherent strength of the support structure 506 may beoffset by expansion forces 524 exerted by the compressed air 526 that iscontained within the chamber 518. Specifically, in a manner analogous tothe stiffening of walls of an inflated balloon, the expansion force ofthe compressed air may contribute additional strength to the supportstructure. This expansion effect is shown grossly exaggerated in FIG. 5,for purposes of illustration.

One possible application for such a design, employs a support structurethat is fabricated from a material that is capable of at least someflexion, for example carbon fiber. In such an embodiment, expansionforces from the compressed air within the chamber of a flexible supportmember, may act against the walls of the chamber, thereby stiffening itand contributing to the structural stability of that support. Such asupport structure could alternatively be formed from other materials,and remain within the scope of the present invention.

A design incorporating carbon fiber could offer even further advantages.For example, carbon fiber structures may exhibit enhanced strength inparticular dimensions, depending upon the manner of their fabrication.Thus, a carbon fiber support structure could be fabricated to exhibitstrength and/or flexion in particular dimensions, for example those inwhich the expansion forces of the compressed air are expected tooperate, and/or dimension in which the support is expected to experienceexternal stress (e.g. a prevailing wind direction).

Of course, a design taking advantage of expansion forces of the storedcompressed air, would need to exhibit sufficient inherent strength inthe face of expected (and unexpected) changes in the quantity ofcompressed air stored therein, as that compressed air is drawn away andallowed to expand for energy recovery. Nevertheless, expansion forcesassociated with minimal amounts of compressed air remaining within thesupport structure, could impart sufficient stability to supportstructure to reduce its cost of manufacture and maintenance.

What is claimed is:
 1. An apparatus comprising: a gascompressor/expander configured to be operated by a wind turbine and influid communication with a compressed gas storage unit; a firstmechanical linkage configured to communicate with the gascompressor/expander; a second mechanical linkage configured tocommunicate energy from the wind turbine; wherein the wind turbine is inmechanical communication with the first mechanical linkage through agear system, wherein the gear system comprises a planetary gear; andwherein the gear system is in communication with an electrical generatorthrough a third mechanical linkage to allow movement of the firstmechanical linkage, the second mechanical linkage, and the thirdmechanical linkage at a same time in an additive manner, and wherein thegear system allows movement of fewer than all of the first mechanicallinkage, the second mechanical linkage, and the third mechanicallinkage.
 2. An apparatus as in claim 1 wherein the gascompressor/expander is located outside a nacelle of the wind turbine. 3.An apparatus as in claim 1 wherein the compressed gas storage unit islocated outside a nacelle of the wind turbine.
 4. An apparatus as inclaim 1 wherein the electrical generator is located outside a nacelle ofthe wind turbine.
 5. An apparatus as in claim 1 wherein the gear systemis located outside a nacelle of the wind turbine.
 6. An apparatus as inclaim 1 wherein the first mechanical linkage comprises a rotatableshaft.
 7. An apparatus as in claim 1 wherein the second mechanicallinkage comprises a rotatable shaft.
 8. An apparatus as in claim 1wherein the third mechanical linkage comprises a rotatable shaft.
 9. Anapparatus as in claim 1 wherein the gas compressor/expander is locatedin a tower with the gear system.